Room temperature curable organopolysiloxane compositions

ABSTRACT

A room temperature curable organopolysiloxane composition comprising (a) an organopolysiloxane having a specific structure, (b) a alkenoxysilane or substituted alkenoxysilane or a partial hydrolyzate thereof, and (c) a siloxane or a partial hydrolyzate thereof cures into a product which experiences no decline of insulation resistance upon application of voltage in a hot humid environment and is resistant to electrolytic corrosion.

[0001] This invention relates to one-part room temperature curableorganopolysiloxane compositions having improved electrical properties,especially resistance to electrolytic corrosion.

BACKGROUND OF THE INVENTION

[0002] In the prior art, one-part room temperature curableorganopolysiloxane compositions are applied to circuit boards forelectric and electronic applications and used as the moisture-proof andanti-fouling coat. A problem arises that the cured organopolysiloxanecompositions experience a decline of insulation resistance uponapplication of voltage in a hot humid environment.

SUMMARY OF THE INVENTION

[0003] An object of the present invention is to provide a one-part roomtemperature curable organopolysiloxane composition which has eliminatedthe drawbacks of the prior art compositions, and cures into a productwhich is resistant to electrolytic corrosion in that no decline ofinsulation resistance occurs upon application of voltage in a hot humidenvironment.

[0004] It has been found that a room temperature curableorganopolysiloxane composition comprising (a) an organopolysiloxanehaving a specific structure, (b) a alkenoxysilane or substitutedalkenoxysilane or a partial hydrolyzate thereof, and (c) a siloxane or apartial hydrolyzate thereof cures into a product which does experienceno decline of insulation resistance upon application of voltage in a hothumid environment and is resistant to electrolytic corrosion.

[0005] Accordingly, the present invention provides a room temperaturecurable organopolysiloxane composition comprising

[0006] (a) 100 parts by weight of an organopolysiloxane having thefollowing general formula (I):

[0007]  wherein R¹ is hydrogen, a substituted or unsubstituted alkylradical or a substituted or unsubstituted alkenyl radical, R² isindependently a substituted or unsubstituted monovalent hydrocarbonradical, X is an oxygen atom or a divalent hydrocarbon radical, a is 0,1 or 2, and n is an integer of at least 10,

[0008] (b) 1 to 30 parts by weight of a substituted or unsubstitutedalkenoxysilane having the following general formula (II):

[0009]  wherein R³ is a substituted or unsubstituted monovalenthydrocarbon radical, R⁴ and R⁵ are each independently hydrogen or asubstituted or unsubstituted monovalent hydrocarbon radical, and x is 3or 4, or a partial hydrolyzate thereof, and

[0010] (c) 0.01 to 10 parts by weight of a siloxane containing permolecule at least one monovalent radical having the general formula(III):

[0011]  wherein R⁶, R⁷, R⁸ and R⁹ each are hydrogen or a monovalenthydrocarbon radical, and y is an integer of 1 to 6, at least two siliconatoms, and at least three radicals selected from the group consisting ofalkyl, alkoxy and alkenoxy radicals, or a partial hydrolyzate thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] Component (a) serving as the base in the composition of theinvention is an organopolysiloxane having the following general formula(I).

[0013] Herein, R¹ is hydrogen, a substituted or unsubstituted alkylradical, preferably having 1 to 10 carbon atoms, more preferably 1 to 8carbon atoms, or a substituted or unsubstituted alkenyl radical,preferably having 2 to 10 carbon atoms, more preferably 2 to 8 carbonatoms. R² which may be the same or different is a substituted orunsubstituted monovalent hydrocarbon radical, preferably having 1 to 10carbon atoms. X is an oxygen atom or a divalent hydrocarbon radical,preferably having 1 to 10 carbon atoms. The letter “a” is 0, 1 or 2, andn is an integer of at least 10.

[0014] More particularly, of the radicals represented by R¹, suitablealkyl radicals include, but are not limited to, methyl, ethyl, propyl,and butyl, and substituted ones of these alkyl radicals in which some orall of the hydrogen atoms are substituted with halogen atoms, cyano orthe like, for example, halogenated alkyl radicals such as chloromethyl,trichloropropyl and trifluoropropyl and cyanoalkyl radicals such as2-cyanoethyl, 3-cyanopropyl and 2-cyanobutyl. Of these, methyl and ethylare preferred. Suitable alkenyl radicals include alkenyl radicals suchas vinyl, allyl and isopropenyl, and substituted ones of these alkenylradicals in which some or all of the hydrogen atoms are substituted witharyl radicals (e.g., phenyl), such as phenylethenyl. Of these,isopropenyl and vinyl are preferred. It is preferred that “a” be 2 whereR¹ is hydrogen, and “a” be 0 or 1 where R¹ is an alkyl or alkenylradical.

[0015] The hydrocarbon radicals represented by R² include, but are notlimited to, alkyl radicals such as methyl, ethyl, propyl, isopropyl,butyl, 2-ethylbutyl and octyl; cycloalkyl radicals such as cyclohexyland cyclopentyl; alkenyl radicals such as vinyl and allyl; aryl radicalssuch as phenyl, tolyl, xylyl, naphthyl, biphenyl and phenanthryl;aralkyl radicals such as benzyl and phenylethyl; and substituted ones ofthe foregoing radicals in which some or all of the hydrogen atoms aresubstituted with halogen atoms, cyano or the like, for example,halogenated hydrocarbon radicals such as chloromethyl, trichloropropyl,trifluoropropyl, bromophenyl and chlorocyclohexyl, and cyano hydrocarbonradicals such as 2-cyanoethyl, 3-cyanopropyl and 2-cyanobutyl. Of these,methyl is preferred.

[0016] X is an oxygen atom or an alkylene radical such as methylene,ethylene and propylene, with the oxygen and ethylene being preferred.

[0017] Preferably, the organopolysiloxane is capped with a hydroxylradical at either end of its molecular chain, especially with onehydroxyl radical at each end of its molecular chain.

[0018] In formula (1), n is an integer of 10 or greater. Theorganopolysiloxane preferably has a viscosity of about 25 to 1,000,000centistokes (cSt) at 25° C., and more preferably about 500 to 500,000cSt at 25° C.

[0019] Component (b) serving as a curing agent in the inventivecomposition is an alkenoxysilane or substituted alkenoxysilane havingthe following general formula (II) or a partial hydrolyzate thereof.

[0020] Herein, R³ is a substituted or unsubstituted monovalenthydrocarbon radical, preferably having 1 to 10 carbon atoms. R⁴ and R⁵which may be the same or different are hydrogen or substituted orunsubstituted monovalent hydrocarbon radicals, preferably having 1 to 10carbon atoms. The letter x is 3 or 4.

[0021] More particularly, suitable hydrocarbon radicals represented byR³ include alkyl, alkenyl, aryl and other radicals as exemplified abovefor R². The monovalent hydrocarbon radicals represented by R⁴ and R⁵include alkyl, alkenyl and other radicals as exemplified above for R².

[0022] Illustrative, non-limiting examples of the alkenoxysilane (b)include methyltrivinyloxysilane, methyltri(isopropenyloxy)silane,vinyltri(isopropenyloxy)silane, phenyltri(isopropenyloxy)silane,propyltri(isopropenyloxy) silane, tetra(isopropenyloxy)silane,methyltri(1-phenylethenyloxy)silane, methyltri(1-butenyloxy)silane,methyltri (1-methyl-1-propenyloxy)silane,methyltri(1,4-dimethyl-1,3-pentadienyloxy)silane and partialhydrolyzates thereof.

[0023] Usually, the alkenoxysilane (b) is added in an amount of 1 to 30parts, preferably 3 to 20 parts, and more preferably 3 to 10 parts byweight per 100 parts by weight of the organopolysiloxane (a). Less than1 part of component (b) effects insufficient crosslinking, failing toprovide the desired rubbery elasticity in the cured state. More than 30parts of component (b) entails an increased shrinkage factor uponcuring, resulting in poor mechanical properties.

[0024] Component (c) serving as a curing catalyst in the inventivecomposition is a siloxane or a partial hydrolyzate thereof. The siloxaneshould contain per molecule at least one monovalent radical having thegeneral formula (III), at least two silicon atoms, and at least threeradicals selected from among alkyl, alkoxy and alkenoxy radicals.

[0025] Herein R⁶, R⁷, R⁸ and R⁹ each are hydrogen or a monovalenthydrocarbon radical, preferably having 1 to 10 carbon atoms, and y is aninteger of 1 to 6. Examples of the monovalent hydrocarbon radicalsrepresented by R⁶, R⁷, R⁸ and R⁹ include those exemplified above for R².

[0026] Preferably, the siloxane (c) has the following general formula(IV).

[0027] Herein R⁶, R⁷, R⁸, R⁹ and y are as defined in formula (III). R¹⁰which may be the same or different is hydrogen, a monovalent hydrocarbonradical, preferably having 1 to 10 carbon atoms, or a radical of theformula:

[0028] wherein R¹¹ is a substituted or unsubstituted monovalenthydrocarbon radical, preferably having 1 to 10 carbon atoms, R¹² is amonovalent hydrocarbon radical, preferably having 1 to 10 carbon atoms,and b is 0, 1 or 2. The letter z is an integer of 1 to 5.

[0029] Examples of the hydrocarbon radicals represented by R¹⁰, R¹¹ andR¹² include those exemplified above for R². R¹² is preferably selectedfrom alkyl and alkenyl radicals.

[0030] Preferred examples of the siloxane (c) are given below.

[0031] In the formulae, Me is methyl, Et is ethyl, Pr is propyl, Ph isphenyl, and z is an integer of 1 to 5.

[0032] Among others, those siloxanes of the formula:

[0033] wherein Me is methyl and z is an integer of 1 to 5 are mostpreferred because of ease of synthesis and rapid film formation (a shorttack-free time).

[0034] Usually, the siloxane (c) is added in an amount of 0.01 to 10parts, preferably 0.1 to 5 parts, and more preferably 0.5 to 4 parts byweight per 100 parts by weight of the organopolysiloxane (a). With lessthan 0.01 part of component (c), a longer time is taken for filmformation (a longer tack-free time). More than 10 parts of component (c)extremely quickens film formation or shortens the tack-free time,resulting in difficulty of working.

[0035] If necessary, numerous fillers may be blended in the inventivecomposition. Suitable fillers include finely divided silica, silicaaerogel, precipitated silica, diatomaceous earth; metal oxides such asiron oxide, zinc oxide, titanium oxide, and aluminum oxide; metalcarbonates such as calcium carbonate, magnesium carbonate and zinccarbonate; asbestos, glass wool, carbon black, fine mica, fused silicapowder, and powdered synthetic resins such as polystyrene, polyvinylchloride, and polypropylene. The fillers may be blended in any desiredamount as long as this does not compromise the objects of the invention.It is preferred that the fillers be dried to remove water before use. Ifdesired, the composition may further include pigments, dyes,antidegradants, antioxidants, antistatic agents, flame retardants (e.g.,antimony oxide and chlorinated paraffin), and thermal conductivitymodifiers (e.g., boron nitride).

[0036] Other additives that can be incorporated in the inventivecomposition include thixotropic agents such as polyether,mildew-proofing agents, antibacterial agents, and adhesive aids,examples of which are aminosilanes such as γ-aminopropyltriethoxysilaneand 3-(2-aminoethylamino)propyltrimethoxysilane, and epoxysilanes suchas γ-glycidoxypropyltrimethoxysilane andβ-(3,4-epoxycyclo-hexyl)ethyltrimethoxysilane. In particular, theaminosilane is added in an amount of preferably 0.1 to 10 parts, morepreferably 0.2 to 5 parts by weight per 100 parts by weight of theorganopolysiloxane (a).

[0037] If necessary, hydrocarbon solvents such as toluene and petroleumether, ketones and esters may be added as the diluent.

[0038] The inventive composition is obtained by intimately mixing theessential components (a) to (c) and optionally, fillers, variousadditives, diluents and the like in a dry atmosphere.

[0039] The inventive composition remains stable in the sealed state, butwhen exposed to air, rapidly cures with airborne moisture and firmlyadheres to numerous substrates. The composition thus finds effective usein a wide variety of applications as a sealing agent, coating agent,adhesive, coating, water repellent, fiber or fabric treating agent, andparting agent.

EXAMPLE

[0040] Examples of the invention are given below by way of illustrationand not by way of limitation. All parts are by weight. It is noted thatthe siloxane prepared in Reference Example was used in Examples andComparative Examples.

Reference Example

[0041] A 1-liter four-necked flask equipped with a thermometer, stirrer,condenser, nitrogen gas inlet and outlet tubes was charged with 278 g (1mol) of 1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine and459 g (3 mol) of tetramethoxysilane, which were stirred and mixed atroom temperature. With stirring continued, 27 g (1.5 mol) of water wasadded dropwise. The flask was then heated at 90-100° C., at which thereaction mixture was ripened for 2 hours. Stripping at 120-130° C. and20 mmHg under nitrogen bubbling yielded 442 g of a product (yield 60%).

[0042] This product was a pale yellow liquid having a viscosity η of 16mPa·s at 23° C., a specific gravity d of 1.06 at 23° C., and arefractive index n_(D) of 1.435 at 25° C. On ²⁹Si NMR spectroscopy,there appeared a peak attributable to —(CH₂)₃—SiO_(1/2)(—OMe)₂ at −49ppm, and a peak attributable to —(CH₂)₃—SiO_(2/2)(—OMe) at −58 ppm, buta peak attributable to —(CH₂)₃—Si(—OMe)₃ at −41 ppm was absent. Based onthese data, the product was identified to be a siloxane of the followingformula wherein Me is methyl and z is an integer of 1 to 5.

Example 1

[0043] A composition was prepared by mixing 100 parts ofdimethylpolysiloxane capped with a hydroxyl radical at either end of itsmolecular chain and having a viscosity of 700 cSt at 25° C. with 8 partsof phenyltri(isopropenyloxy)silane, 1 part of3-aminopropyltriethoxysilane and 1.5 parts of the siloxane obtained inReference Example, in a dry state, followed by deaeration and mixing.

[0044] Physical properties of the composition were determined, with theresults shown below. Tack-free time 4 min Hardness (Durometer type A) 27Elongation at break 50% Electrolytic corrosion resistance see Table 1

[0045] It is noted that the tack-free time, Durometer type A hardnessand elongation at break were measured according to JIS K6249. Theelectrolytic corrosion resistance was determined by applying 1 ml of thecomposition to JIS-B interdigital electrodes so as to cover theelectrode surface, and holding the coating at 23° C., RH 50% for one dayfor curing. The coated electrode structure was then placed in athermostat chamber held at 80° C. and RH 90%, where the insulationresistance was measured at predetermined time intervals by applying a DCvoltage of 12 volts across the electrodes.

Example 2

[0046] A composition was prepared by mixing 100 parts ofdimethylpolysiloxane capped with a trimethoxysilyl radical at either endof its molecular chain and having a viscosity of 20,000 cSt at 25° C.with 8 parts of vinyltri(isopropenyloxy)silane, 1 part of3-aminopropyltriethoxysilane and 1.5 parts of the siloxane obtained inReference Example, in a dry state, followed by deaeration and mixing.

[0047] Physical properties of the composition were determined as inExample 1, with the results shown below. Tack-free time 8 min Hardness(Durometer type A)  20 Elongation at break 300% Electrolytic corrosionresistance see Table 1

Example 3

[0048] A composition was prepared by mixing 100 parts ofdimethylpolysiloxane capped with a diisopropenoxyvinylsilyl radical ateither end of its molecular chain and having a viscosity of 20,000 cStat 25° C. with 4 parts of vinyltri(isopropenyloxy)silane, 1 part of3-aminopropyltriethoxysilane and 1.5 parts of the siloxane obtained inReference Example, in a dry state, followed by deaeration and mixing.

[0049] Physical properties of the composition were determined as inExample 1, with the results shown below. Tack-free time 8 min Hardness(Durometer type A)  20 Elongation at break 150% Electrolytic corrosionresistance see Table 1

Example 4

[0050] 100 parts of dimethylpolysiloxane capped with a hydroxyl radicalat either end of its molecular chain and having a viscosity of 5,000 cStat 25° C. was mixed with 5 parts of fumed silica. The mixture wasagitated and mixed in vacuum at 150° C. for 2 hours. Then 60 parts ofcrystalline silica was added to the mixture, which was agitated andmixed in vacuum at room temperature for 30 minutes. This was furthermixed with 8 parts of phenyltri(isopropenyloxy)silane, 1 part of3-(2-aminoethyl-amino)propyltriethoxysilane and 2 parts of the siloxaneobtained in Reference Example, in a dry state, followed by deaerationand mixing.

[0051] Physical properties of the resulting composition were determinedas in Example 1, with the results shown below. Tack-free time 5 minHardness (Durometer type A)  50 Elongation at break 200% Electrolyticcorrosion resistance see Table 1

Comparative Example 1

[0052] A composition was prepared as in Example 1 except that 1 part of1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine was usedinstead of 1.5 parts of the siloxane obtained in Reference Example.Physical properties of the composition were similarly determined, withthe results shown below. Tack-free time 4 min Hardness (Durometer typeA) 28 Elongation at break 50% Electrolytic corrosion resistance seeTable 1

Comparative Example 2

[0053] A composition was prepared as in Example 2 except that 1 part of1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine was usedinstead of 1.5 parts of the siloxane obtained in Reference Example.Physical properties of the composition were similarly determined, withthe results shown below. Tack-free time 8 min Hardness (Durometer typeA)  22 Elongation at break 280% Electrolytic corrosion resistance seeTable 1

Comparative Example 3

[0054] A composition was prepared as in Example 3 except that 1 part of1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine was usedinstead of 1.5 parts of the siloxane obtained in Reference Example.Physical properties of the composition were similarly determined, withthe results shown below. Tack-free time 9 min Hardness (Durometer typeA)  21 Elongation at break 160% Electrolytic corrosion resistance seeTable 1

Comparative Example 4

[0055] A composition was prepared as in Example 4 except that 2 parts of1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine was usedinstead of 2 parts of the siloxane obtained in Reference Example.Physical properties of the composition were similarly determined, withthe results shown below. Tack-free time 6 min Hardness (Durometer typeA)  55 Elongation at break 180% Electrolytic corrosion resistance seeTable 1

[0056] TABLE 1 Insulation resistance when aged at 80° C. RH 90% ExampleComparative Example 1 2 3 4 1 2 3 4 Initial ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ 1 hr ≧1000 MΩ ≧1000 MΩ≧1000 MΩ ≧1000 MΩ   20 MΩ   20 MΩ   20 MΩ   20 MΩ 1 day ≧1000 MΩ ≧1000MΩ ≧1000 MΩ ≧1000 MΩ   30 MΩ   30 MΩ   20 MΩ   50 MΩ 2 days ≧1000 MΩ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ   50 MΩ   40 MΩ   30 MΩ  100 MΩ 7 days ≧1000MΩ ≧1000 MΩ ≧1000 MΩ ≧1000 MΩ   70 MΩ   80 MΩ   50 MΩ  200 MΩ

[0057] It is evident that the one-part room temperature curableorganopolysiloxane compositions of the invention cure into productswhich are resistant to electrolytic corrosion in that no decline ofinsulation resistance occurs upon application of voltage in a hot humidenvironment.

[0058] Japanese Patent Application No. 2001-196122 is incorporatedherein by reference.

[0059] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A room temperature curable organopolysiloxane composition comprising(a) 100 parts by weight of an organopolysiloxane having the followinggeneral formula (I):

 wherein R¹ is hydrogen, a substituted or unsubstituted alkyl radical ora substituted or unsubstituted alkenyl radical, R² is independently asubstituted or unsubstituted monovalent hydrocarbon radical, X is anoxygen atom or a divalent hydrocarbon radical, a is 0, 1 or 2, and n isan integer of at least 10, (b) 1 to 30 parts by weight of a substitutedor unsubstituted alkenoxysilane having the following general formula(II):

 wherein R³ is a substituted or unsubstituted monovalent hydrocarbonradical, R⁴ and R⁵ are each independently hydrogen or a substituted orunsubstituted monovalent hydrocarbon radical, and x is 3 or 4, or apartial hydrolyzate thereof, and (c) 0.01 to 10 parts by weight of asiloxane containing per molecule at least one monovalent radical havingthe general formula (III):

 wherein R⁶, R⁷, R⁸ and R⁹ each are hydrogen or a monovalent hydrocarbonradical, and y is an integer of 1 to 6, at least two silicon atoms, andat least three radicals selected from the group consisting of alkyl,alkoxy and alkenoxy radicals, or a partial hydrolyzate thereof.
 2. Theorganopolysiloxane composition of claim 1 wherein the organopolysiloxane(a) is capped with a hydroxyl radical at either end of its molecularchain.
 3. The organopolysiloxane composition of claim 1 wherein thesiloxane (c) has the following general formula (IV):

wherein R⁶, R⁷, R⁸, R⁹ and y are as defined above, R¹⁰ is independentlyhydrogen: a monovalent hydrocarbon radical or a radical of the formula:

wherein R¹¹ is a substituted or unsubstituted monovalent hydrocarbonradical, R¹² is a monovalent hydrocarbon radical, and b is 0, 1 or 2,and z is an integer of 1 to 5.